Southern Nuclear Operating Company is in the process of putting a nuclear reactor back online at the Alvin W. Vogtle Electric Generating Plant in Waynesboro today, after it unexpectedly shut down on Monday.

The plant is currently operating at three percent of its capacity, according to Southern and the U.S. Nuclear Regulatory Commission, although both declined to say when the reactor would return to normal operation.

A breaker on an electrical switchgear opened, causing a loss of vacuum that is required to produce steam, according to a spokesman for the NRC. The steam, in turn, powers a turbine that initiates the production of electricity.

Workers are still investigating what caused the breaker to open.

The equipment failure happened on a side of the reactor not directly involved in the actual nuclear production process. The reactor shut down automatically, as it is designed to, on Monday as a safety precaution, and the issue caused no danger.

The company has utilized other sources of energy, including its coal and natural gas plants, to supply power during the shutdown. Vogtle's other reactor is still operating.

Each reactor at Vogtle powers more than 300,000 homes.

Nuclear reactors are typically shut down periodically for maintenance. But unplanned shutdowns are uncommon; the NRC says that the industry-wide rate is less than one per year at each plant, although some plants have more and some have less.

Vogtle has had no other unplanned shutdowns at either reactor from the last quarter of 2007 until now, according to the NRC's website, and officials did not immediately know when the last one occurred.

Also, the NRC released information yesterday about potential problems with silver sulfide corrosion on a part of a component that controls the speed of turbines in nuclear reactors. The issue, which is not considered major, was discovered earlier this year and affects equipment on reactors at Vogtle and the Callaway nuclear plant near Fulton, Missouri, about 100 miles west of St. Louis. Workers at each plant either replaced the part or were advised to monitor it.

Officials didn't think the issue was related to the reactor shutdown at Vogtle on Monday.

Georgia Power is a majority owner of Plant Vogtle, which is operated by Southern Nuclear. Both groups are a part of Southern Company, based in Birmingham. The company is currently seeking approval from the NRC to build two more nuclear reactors there.